Organic light emitting device

ABSTRACT

An organic light emitting device includes a transistor having gate, source, and drain electrodes, and first electrode connected to one of the source or drain electrodes. The device also includes an emitting layer positioned on the first electrode and a second electrode positioned on the emitting layer. Each of the source and drain electrodes includes first, second, and third layers having different tapered angles. The first electrode may include a metallic layer and a conductive layer, with a tapered angle of the metallic layer being different from a tapered angle of the conductive layer.

This application is a continuation of U.S. patent application Ser. No.11/987,750 filed Dec. 4, 2007, which claims the benefit of Korean PatentApplication Nos. 10-2007-0121546 and 10-2007-0121542 both filed Nov. 27,2007, the subject matters of which are incorporated herein by reference.

BACKGROUND

1. Field

One or more embodiments described herein relate to a display device.

2. Background

The importance of flat panel displays has recently increased withconsumer demand for multimedia products and services. An organic lightemitting device (OLED) is desirable because it has a rapid responsetime, low power consumption, self-emission structure, and wide viewingangle. In spite of their many advantages, OLEDs tend to have non-uniformluminance characteristics which degrade reliability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of one embodiment of an organic light emitting device.

FIG. 2 is a sectional view of a sub-pixel that may be included in theorganic light emitting device of FIG. 1.

FIG. 3 is an enlarged view showing one example of a source or drainelectrode that may be included in region ‘A’ in FIG. 2.

FIG. 4 is a view showing another example of a source or drain electrodethat may be included in region ‘A’ in FIG. 2.

FIG. 5 is a view showing another example of a source or drain electrodethat may be included in region ‘A’ in FIG. 2.

FIG. 6 is a view showing another example of a source or drain electrodethat may be included in region ‘A’ in FIG. 2.

FIG. 7 is a view showing one example of a first electrode that may beincluded in region ‘B’ in FIG. 2.

FIG. 8 is a view showing another example of a first electrode that maybe included in region ‘B’ in FIG. 2.

FIGS. 9A to 9C illustrate various implementations of a color imagedisplay method in an organic light emitting device according to anexemplary embodiment.

DETAILED DESCRIPTION

An organic light emitting diode incorporated within an organic lightemitting device is a self-emission device in which a light emissionlayer is formed between two electrodes positioned on a substrate.Generally, there are several types of OLEDs: a top-emission type, abottom-emission type, and a dual-emission type. These devices maydiffer, for example, based on the direction in which light is emitted.OLEDs may also be classified as passive matrix or active matrix devices.

In operation, scan, data, and power signals supplied to a sub-pixelsdisposed in matrix form generate light which form an image. In one typeof OLED, a thin film is formed on a substrate and patterned to formwirings and electrodes. Because the wirings or electrodes are formed assingle layers, step coverage may be degraded. In addition, when a signalor power is applied, wire resistance tends to be high, thereby degradingdisplay quality and reliability.

FIG. 1 shows one embodiment of an organic light emitting device. Thisdevice includes a display part 120 with a plurality of sub-pixels (P)positioned thereon on a substrate 110. The sub-pixels positioned on thesubstrate are susceptible to moisture or oxygen. Thus, a sealingsubstrate 130 is provided and an adhesive member 140 is formed at outeredge portions of the substrate of the display part 120 to seal thesubstrate and sealing substrate. Meanwhile, the sub-pixels may be drivenby a driver 150 positioned on the substrate. The driver generatessignals to cause an image to be displayed.

The sub-pixels (P) may emit red, green, or blue. Preferably, sub-pixelsemitting all three colors are grouped to define a single unit pixelwithin the device. Alternatively, or additionally, each unit pixel maybeformed from one or more sub-pixels that emit white light, white light incombination with sub-pixels that emit red, green, and blue light, and/orthe one or more of the aforementioned combinations of sub-pixels takenwith sub-pixels that emit other colors, e.g., orange, yellow, etc.According to one embodiment, a unit pixel may therefore be formed fromfour sub-pixels that emit light of different colors, e.g., white, red,green, and blue. In still another embodiment, white pixels may be usedwith one or more color filters to generate light of various combinationsof colors. In this latter embodiment, light from the white sub-pixelsmay also be allowed to pass unfiltered.

In terms of structure, all or a portion of the sub-pixels forming eachunit pixel may comprise an emitting layer. The emitting layer may beformed from or coupled with a hole injection layer, hole transportlayer, electron transport layer, electron transport layer, or variouscombinations thereof. The sub-pixels may also include a buffer layerand/or a blocking layer that controls the flow of holes or electrodesbetween anode and cathode electrodes.

The sub-pixels may further include an organic light emitting diode(OLED) connected with a source or drain electrode of a drivingtransistor included in a transistor array positioned on substrate 110.The transistor array may comprise one or more transistors andcapacitors, and each of the transistors in the array may include aswitching transistor that switches a scan signal and the drivingtransistor that drives a data signal.

FIG. 2A shows a sectional view of one embodiment of a sub-pixel of theorganic light emitting device in FIG. 1. In forming thesub-pixel/device, substrate 110 may be made of a material having goodmechanical strength and size stability. For example, the substrate maybe made from a glass plate, a metal plate, a ceramic plate, a plasticplate (e.g., a polycarbonate resin, acryl resin, vinyl chloride resin,polyethylene terephthalate resin, polyimide resin, polyester resin,epoxy resin, silicon resin, fluorine resin, etc.), or the like.

A buffer layer 111 may be positioned on the substrate. This layer may beformed to protect a TFT to be formed in a follow-up process againstimpurities such as alkali ions generated from the substrate. The bufferlayer may be made, for example, of silicon oxide (SiO₂) or siliconnitride (SiNx).

A semiconductor layer 112 may be positioned on the buffer layer and maybe made of amorphous silicon or polycrystalline silicon obtained bycrystallizing amorphous silicon. Although not shown, the semiconductorlayer may include a channel region, source region, and drain region.P-type or N-type impurities may be doped into the source or drainregions.

A gate insulating layer 113 may be positioned on the substrate withsemiconductor layer 112 formed thereon. The gate insulating layer may beformed by selectively using silicon oxide (SiO₂) or silicon nitride(SiNx).

A gate electrode 114 may be positioned on the gate insulating layer 113at a location that corresponds, for example, to the channel region oranother region of semiconductor layer 112. The gate electrode may bemade of aluminum (Al), an aluminum (Al) alloy, titanium (Ti), silver(Ag), molybdenum (Mo), a molybdenum (Mo) alloy, tungsten (W), ortungsten silicide (WSi₂) or a combination thereof.

An interlayer insulating layer 115 may be positioned over the substrateincluding gate electrode 114 formed thereon. The interlayer insulatinglayer may be or include an organic layer or an inorganic layer, or acomposite layer comprising an organic layer and an inorganic layer.

When the interlayer insulating layer is or includes an inorganic layer,it may be made of silicon oxide (SiO₂), silicon nitride (SiNx), or SOG(Silicate On Glass). When the interlayer insulating layer is or includesan organic layer, it may comprise an acrylic resin, a polyimide resin,or a benzocyclobutene (BCB) resin. First and second contact holes 115 aand 115 b that expose portions of semiconductor layer 112 may bepositioned within interlayer insulation layer 115 and gate insulatinglayer 113.

A first electrode 116 a may be positioned on the interlayer insulatinglayer. The first electrode may be an anode and formed to have asingle-layer structure comprising a conductive layer made of such as ITO(Indium Tin Oxide) or IZO (Indium Zinc Oxide). Alternatively, the firstelectrode may be formed to have a multi-layer structure comprising aconductive layer made of such as ITO or IZO.

A source electrode 116 b and drain electrode 116 c may be positioned onthe interlayer insulating layer. The source and drain electrodes 116 band 116 c may be electrically connected via first and second contactholes 115 a and 115 b. A portion of the drain electrode 116 c ispositioned on the first electrode 116 a and electrically connected withthe first electrode 116 a.

The source and drain electrodes 116 b and 116 c may contain a lowresistance material. Also, the source and drain electrodes may be formedto have a multi-layer structure that includes a metallic layer made, forexample, of aluminum (Al), Alnd, molybdenum (Mo), chromium (Cr), TiN,MoN, or CrN.

The transistor on substrate 110 may include gate electrode 114 andsource and drain electrodes 116 b and 116 c, and the transistor arraymay include the plurality of transistors and capacitors which areelectrically connected with the organic light emitting diode (OLED).

An insulating layer 117 exposing a portion of first electrode 116 a maybe positioned on the first electrode, which, for example, may be ananode. The insulating layer may be made of an organic material such asbenzocyclobutene (BCB) resin, acrylic resin, or polyimide resin.

An emitting layer 118 may be positioned on the exposed first electrode116 a, and a second electrode 119 (e.g., a cathode) may be positioned onthe emitting layer. The second electrode may be a cathode that supplieselectrodes to the emitting layer and may be made of magnesium (Mg),silver (Ag), calcium (Ca), aluminum (Al), or their alloys.

In accordance with one embodiment, the organic light emitting diode(connected with source electrode 116 b or drain electrode 116 c) maycomprise the first electrode 116 a, the emitting layer 118 and thesecond electrode 119.

With reference to FIG. 2B, unlike the case as shown in FIG. 2A, thefirst electrode 116 a positioned on the source or drain electrode 116 bor 116 c may be positioned on a planarization film 117 a that planarizesthe surface of the transistor array.

In this case, an insulating layer 117 b may be positioned to expose aportion of the first electrode 116 a (e.g., an anode) on theplanarization film 117 a.

The first electrode 116 a positioned on the source electrode 116 b ordrain electrode 116 c may be positioned on a planarization film thatplanarizes the surface of the transistor array. The structure of thetransistors of the transistor array may vary based on whether a gatestructure is a top gate or a bottom gate. In addition, the structure ofthe transistors may vary depending on number of masks used for formingthe transistor array and the material of the semiconductor layer. Inother embodiments, the sub-pixels may have a different structure.

FIG. 3 shows one example of a source or drain electrode in a region ‘A’of FIG. 2. For the sake of explanation, the description will be focusedon the source electrode 116 b as shown in the region ‘A’. However, thestructure as shown in the region ‘A’ can be also applied to drainelectrode 116 c as well as to source electrode 116 b. In this respect,the positions of the source and drain electrodes 116 b and 116 c maydiffer according to the structure of the sub-pixels.

The source electrode 116 b (including the drain electrode) as shown inthe region ‘A’ in FIG. 3 may be positioned on interlayer insulatinglayer 115, which is positioned on substrate 110. In addition, the sourceelectrode 116 b (including the drain electrode) may be positioned on adifferent insulating material such as the planarization film, not theinterlayer insulating layer 115.

The source electrode 116 b may be formed to have a three-layer structureby stacking one or more different materials. That is, the sourceelectrode may include first to third layers 116 ba, 116 bb, and 116 bc,each of which have sloped edge portions. In accordance with oneembodiment, at least two of these layers have different tapered angles.In accordance with another embodiment, all three layers have differenttapered angles relative to one another. The tapered angles may bedefined, for example, by the slope of the edge portion of the electrode,e.g., the angle between a lower surface of each layer and the slopededge of that layer.

The first and third layers 116 ba and 116 bc may be made of the samematerial, and the first and second layers 116 ba and 116 bb may be madeof different materials. For example, the stacked structure of the firstto third layers 116 ba, 116 bb, and 116 bc may be made, for example, ofmolybdenum/aluminum/molybdenum (Mo/Al/Mo) or molybdenum/Alnd/molybdenum(Mo/Alnd/Mo).

Also, the first layer 116 ba may be selectively made of metal that canimprove ohmic contact characteristics. The second layer 116 bb may beselectively made of metal that can lower specific resistance. And, thethird layer 116 bc may be selectively made of metal that may not beeasily etched in the process of a different metallic layer.

In accordance with one embodiment, the tapered angle r1 of the firstlayer 116 ba serving as a base may lie within a range of about 30° to50°. When the tapered angle r1 of the first layer 116 ba is 30° orgreater, a step coverage of the first layer can be improved. Inaddition, the formation of the second and third layers 116 bb and 116 bccan be facilitated, as well as the first layer 116 ba at thecorresponding portion defined on the substrate.

If the tapered angle r1 of the first layer 116 ba is 50° or smaller, thefirst layer 116 ba may be formed so as to maintain step coverage of thefirst layer 116 ba. In addition, a contact area with the second layer116 bb formed on the first layer 116 ba may be secured.

A tapered angle r2 of the second layer 116 bb positioned on the firstlayer 116 ba may lie within the range of about 50° to 70°. If thetapered angle r2 of the second layer 116 bb is 50° or greater, the stepcoverage of the second layer 116 bb can be improved. In addition, it canfacilitate the formation of the second layer 116 bb on the correspondinglimited portion of the first layer 116 ba.

If the tapered angle r2 of the second layer 116 bb is 70° or smaller,the second layer 116 bb may be formed on the first layer 116 ba so as tomaintain step coverage of the second layer 116 bb. In addition, acontact area with the third layer 116 bc formed on the second layer 116bb can be obtained.

A tapered angle r3 of the third layer 116 bc positioned on the secondlayer 116 bb may lie within the range of about 70° to 90°. If thetapered angle r3 of the third layer 116 bc is 70° or greater, the stepcoverage of the third layer 116 bc can be improved. In addition, thethird layer 116 bc may be easily formed on the corresponding limitedportion of the second layer 116 bb.

If the tapered angle r3 is 90° or smaller, the third layer 116 bc cancontact with the first electrode 116 a, a pixel electrode, so as tomaintain step coverage. In this case, the third layer 116 bc may beelectrically connected with a portion of the first electrode 116 a, thepixel electrode, as shown in FIG. 2, and this may differ according tohow the thin films are formed. That is, one or more of the first andsecond layers 116 ba and 116 bb, but not the third layer 116 bc, may beelectrically connected with the first electrode 116 a, the pixelelectrode.

When the source and drain electrodes are formed to have such a structureincluding the first to third layers 116 ba, 116 bb and 116 bc, thethickness of each layer may be set based on the second layer 116 bb.

This is because the second layer 116 bb, namely, the intermediate layer,determines attachment (bonding) or contact area and serves to reducewiring resistance between the lower and upper layers, so it isadvantageous to set the thickness of each layer based on the secondlayer 116 bb.

Namely, because the source and drain electrodes are to have a lowresistance to transfer power, it is more advantageous to use the secondlayer positioned between the first and third layers 116 ba and 116 bc byforming it to be thicker, than using the first or third layer 116 ba or116 bc.

Here, the thickness ratio of the first and second layers may be1:2.25˜22.5. And the thickness ratio of the third and second layers maybe 1:1.2˜9.

The thickness of the second layer 116 bb, the intermediate layer, may be450 Å to 4,500 Å, that of the first layer 116 ba may be 20 Å to 200 Å,and that of the third layer may be 50 Å to 500 Å.

The reason why the thickness ratio of the first and second layers is1:2.25˜22.5 is because, with such a thickness ratio, the first layer 116ba may be formed within a range that there is no resistance differencebetween the second and first layers 116 bb and 116 ba and the firstlayer 116 ba may not only serve as an ohmic-contact layer of the sourceand drain electrodes but also serve to improve adhesive strength withthe lower interlayer insulating layer 115. Thus, the first layer 116 bacan be formed to be so thin, compared with the second layer 116 bb, asto sufficiently perform such functions.

The reason why the thickness ratio of the third and second layers is1:1.2˜9 is because, with such a thickness ratio, the third layer 116 bcmay be formed within an range that there is no resistance differencebetween the second and third layers 116 bb and 116 bc, and can be formedto protect the lower second layer 116 bb (e.g., it prevents the secondlayer 116 bb from being etched during an etching process in forming thefirst electrodes of the organic light emitting diode), rather than theaspect of resistance.

Accordingly, the third layer 116 bc may be formed to be so thin,compared with the second layer 116 bb, as to perform such function, butmay be formed to be thicker than the first layer 116 ba.

FIG. 4 shows another embodiment of the source or drain electrode in theregion ‘A’ in FIG. 2. Unlike the source electrode as shown in FIG. 3,the source electrode 116 b shown in FIG. 4 may have such a structurethat the first and third layers 116 ba and 116 bc hermetically seal thesecond layer 116 bb. In this case, the first and third layers 116 ba and116 bc contact directly.

Accordingly, when the first and third layers 116 ba and 116 bc are madeof the same material, their electrical characteristics may be improved.If the first and third layers 116 ba and 116 bc are made of differentmaterials, because they contact directly, a problem of electricalcharacteristics caused by the different materials can be avoided.

FIG. 5 shows another embodiment of the source or drain electrode inregion ‘A’ in FIG. 2. As shown, the source or drain electrode has adual-layer structure. That is, for example, source electrode 116 b mayhave a dual-layer structure as shown in region ‘A’ and may be positionedon interlayer insulating layer 115 on the substrate. The sourceelectrode 116 b may be positioned on a different insulating materialsuch as the planarization film, but not the interlayer insulating layer115.

The source electrode 116 b may be formed such that two layers can bestacked and made of one or more different materials. That is, the sourceelectrode 116 b may comprise first and second layers 116 ba and 116 bb.The first and second layers 116 ba and 116 bb may have different taperedangles. (The tapered angle may be defined by the slope of an edge of thelayer relative to a lower surface of the layer).

The first and second layers 116 ba and 116 bb may be different metalliclayers. For example, the first and second layers 116 ba and 116 bb maybe selected from the group including molybdenum (Mo), aluminum (Al),Alnd, chromium (Cr), TiN, MoN, or CrN. Moreover, the first layer 116 bamay be selectively made of a metal that can improve ohmic contactcharacteristics, and the second layer 116 bb may be selectively made ofmetal that can lower specific resistance.

The tapered angle r1 of the first layer 116 ba may lie within the rangeof about 70° to 90°. When the tapered angle r1 of the first layer 116 bais 70° or greater, critical dimension (CD) bias can be reduced tothereby reduce loss caused by wire resistance. In addition, formation ofthe second layer 116 bb on the first layer 116 ba can be facilitated.When the tapered angle r1 of the first layer 116 ba is 90° or smaller, acontact area with the second layer 116 bb can be secured in a state ofreducing the loss caused by the wire resistance.

The tapered angle r2 of the second layer 116 bb positioned on the firstlayer 116 ba may lie within the range of about 40° to 50°. When thetapered angle r2 of the second layer 116 bb is 40° or greater, the stepcoverage of the second layer can be improved. In addition, the secondlayer 116 bb can be easily formed on the corresponding limited portionof the first layer 116 ba.

When the tapered angle r2 of the second layer 116 bb is 50° or smaller,the second layer 116 bb can be formed on the first layer 116 ba whilemaintaining improved step coverage of the second layer 116 bb. Inaddition, while maintaining the step coverage, the second layer 116 bbcan contact with the first electrode 116 a, the pixel electrode.

When the source and drain electrodes are formed to have such a structureincluding the first and second layers 116 ba and 116 bb, the thicknessratio of the first and second layers may be substantially 4˜6.4:1.

The thickness of the first layer 116 ba may be 400 Å˜450 Å, and that ofthe second layer 116 bb may be 70 Å˜400 Å.

Here, because the source and drain electrodes are to have a lowresistance to transfer power, it is advantageous to form the first layer116 a to be thicker than the second layer 116 bb.

The reason why the thickness ratio of the first and second layers 116 baand 116 bb is 4˜6.4:1 is because, with such a thickness ratio, the firstlayer 116 ba may be formed within a range that there is no resistancedifference between the second and first layers 116 bb and 116 ba and thesecond layer 116 bb may serve to protect the lower first layer 116 ba(e.g., it prevents the first layer 116 ba from being etched during anetching process in forming the first electrodes of the organic lightemitting diode) rather than the aspect of resistance. Thus, the secondlayer 116 bb can be formed to be so thin, compared with the first layer116 ba, as to sufficiently perform such function.

In this case, the second layer 116 bb may be electrically connected witha portion of the first electrode 116 a, the pixel electrode, as shown inFIG. 2, and this may differ according to how the thin films are formed.That is, the first layer 116 ba, but not the second layer 116 bb, may beelectrically connected with the first electrode 116 a, the pixelelectrode.

In accordance with one embodiment, the thickness of the region makingthe tapered angle r2 of the second layer 116 bb may be one-third ortwo-thirds the thickness of the source electrode 116 b. Accordingly, theCD bias can be kept small and wire resistance can be reduced to therebyimprove voltage-current characteristics.

FIG. 6 shows another embodiment of the source or drain electrode inregion ‘A’ in FIG. 2. In this embodiment, the source or drain electrodeis formed as a single layer.

More specifically, the source electrode 116 b having a single-layerstructure as shown in region ‘A’ may be positioned on interlayerinsulating layer 116 positioned on the substrate. However, the sourceelectrode 116 b (including the drain electrode) may be positioned on adifferent insulating material such as the planarization film, but notthe interlayer insulating layer 115. In terms of materials, the sourceelectrode may be made as a single metallic layer of for example,molybdenum (Mo), aluminum (Al), Alnd, chromium (Cr), TiN, MoN, or CrN.

The tapered angle r1 of the source angle 116 b may lie within the rangeof about 10° to 60°. When the tapered angle r1 of the source electrode116 b is 10° or greater, the tapered angle r1 of the source electrode116 b may be reduced while step coverage of the source electrode 116 bcan be improved. When the tapered angle r1 of the source electrode 116 bis 60°, step coverage conditions of the source electrode 116 can bemaintained while the problem of contact deficiency with the firstelectrode 116 a, the pixel electrode, which is to contact with thesource electrode 116 b, can be solved.

FIG. 7 shows an embodiment of the first electrode in region ‘B’ in FIG.2. In this embodiment, the first electrode has a dual-layer structure.Also, the structure of the first electrode 116 a, the pixel electrode,may differ depending on a light emission method, e.g., top-emission typeand bottom-emission type. Also, the material of the first electrode mayvary according to the light emission method. The first electrode mayhave such an inverted structure that the electrode is turned over.

In accordance with one embodiment, the first electrode 116 a in region‘B’ may operate as an anode. Also, the structure in region ‘B’ may beapplied to form a second electrode (not shown), namely a cathode, aswell as for the first electrode 116 a operating as an anode.

The first electrode 116 a as shown in the region ‘B’ in FIG. 7 may bepositioned on the interlayer insulating layer 115 on the substrate.Also, the first electrode 116 a may be positioned on a differentinsulating material such as the planarization film, but not theinterlayer insulating layer 115.

Structurally, the first electrode may be formed as the dual-layer bystacking one or more different materials. The dual-layer structure ofthe first electrode may include a metallic layer 116 aa and a conductivelayer 116 ab on the metallic layer 116 aa. The metallic layer 116 aa maybe made of for example, aluminum (Al) or silver (Ag) and the conductivelayer 116 ab may be made of for example, ITO or IZO.

The metallic layer 116 aa may be selectively made of metal that canobtain low resistance ratio and high reflexibility of about 95% at avisible light region in case of top light emission. The conductive layer116 ab may be selectively made of a conductor that has high adhesivestrength with the metallic layer 116 aa serving as the basis and inconsideration of electrical characteristics with the emitting layerpositioned at an upper portion of the conductive layer 116 ab.

The metallic layer 116 aa and conductive layer 116 ab may have differenttapered angles. (The tapered angle of each layer may be defined by aslope of its edge relative to a lower surface of the layer.) The taperedangle r1 of metallic layer 116 aa may lie within the range of about 35°to 70°. When the tapered angle r1 of metallic layer 116 aa is 35° orgreater, it can facilitate formation of conductive layer 116 ab onmetallic layer 116 aa in a state of securing the upper area of themetallic layer 116 aa. When the tapered angle r1 of metallic layer 116aa is 70° or smaller, the contact area with conductive layer 116 abformed on metallic layer 116 aa can be obtained. In addition, thecontact interface characteristics with the conductive layer 116 ab canbe improved.

The tapered angle r2 of the conductive layer 116 ab positioned onmetallic layer 116 aa may lie within the range of about 70° to 90°. Whenthe tapered angle r2 of the conductive layer 116 ab is 70° or greater,it can facilitate formation of an emitting layer (not shown) on theconductive layer 116 ab so as to secure an aperture area of the emittinglayer (not shown) formed on the conductive layer 116 ab. When thetapered angle r2 of conductive layer 116 ab is 90° or smaller, it canfacilitate formation of the emitting layer (not shown) on the conductivelayer 116 ab so as to secure the aperture area of the emitting layer(not shown) formed on the conductive layer 116 ab to its maximum level.

When the first electrode 116 a is formed to have such a structureincluding the metallic layer 116 aa and the conductive layer 116 ab, thethickness ratio of the two layers may be substantially 9.5˜10:1.

Here, with the ratio of 9.5˜10:1 of the metallic layer 116 aa and theconductive layer 116 ab, the metallic layer 116 aa can serve as areflection layer.

FIG. 8 shows another embodiment of the first electrode in region ‘B’ inFIG. 2. In this embodiment, the first electrode has a triple-layerstructure. Also, the first electrode 116 a as shown in the region ‘B; inFIG. 8 may be positioned on the interlayer insulating layer 116 on thesubstrate. Or, the first electrode 116 a may be positioned on adifferent insulating material such as the planarization film, but notthe interlayer insulating layer 115.

The first electrode 116 a may be formed by stacking one or moredifferent materials. For example, the first electrode 116 a may comprisea first conductive layer 116 aa, a metallic layer 116 ab positioned onthe first conductive layer, and a second conductive layer 116 acpositioned on the metallic layer. The first conductive layer 116 aa,metallic layer 116 ab, and second conductive layer 116 ac may have oneor more tapered angles which are different from each other. (The taperedangles may be defined by the slope formed on the basis of the lowersurface of the edge portion.)

The first and second conductive layers 116 aa and 116 ac may be made of,for example, ITO or IZO, and the metallic layer 116 ab may be made offor example, aluminum (Al) or silver (Ag).

The tapered angle r1 of the first conductive layer 116 aa as the basismay lie within the range of about 50° to 90°. When the tapered angle r1of the first conductive layer 116 aa is 50° or greater, it canfacilitate formation of the second conductive layer 116 ac as well asthe metallic layer 116 ab on the first conductive layer 116 aa in astate of securing the upper area of the first conductive layer 116 aa.When the tapered angle of the first conductive layer 116 aa is 90° orsmaller, the contact area with the metallic layer 116 ab formed on thefirst conductive layer 116 aa can be secured. In addition, the contactinterface characteristics with the metallic layer 116 ab can beimproved.

The tape angle r2 of the metallic layer 116 ab positioned on the firstconductive layer 116 aa may lie within the range of about 35° to 70°.When the tapered angle r2 of the metallic layer 116 ab is 35° orgreater, the area of the second conductive layer 116 ac to be formed onthe metallic layer 116 ab can be secured. When the tapered angle r2 ofthe metallic layer 116 ab is 70° or smaller, the contact area with thesecond conductive layer 116 ac formed on the metallic layer 116 ab canbe secured in the state that the upper area of the metallic layer 116 abis secured.

The tapered angle r3 of the second conductive layer 116 ac positioned onthe metallic layer 116 ab may lie within the range of 70° to 90°. Whenthe tapered angle r3 of the second conductive layer 116 ac is 70° orgreater, in a state where an aperture area of the emitting layer (notshown) formed on the second conductive layer 116 ac is secured, theemitting layer (not shown) can be easily formed on the second conductivelayer 116 ac.

When the tapered angle r3 of the second conductive layer 116 ac is 90°,in the state where the aperture area of the emitting layer (not shown)formed on the second conductive layer 116 ac is secured to a maximumlevel, the emitting layer (not shown) can be easily formed on the secondconductive layer 116 ac.

When the first electrode 116 a is formed to have such structureincluding the first conductive layer 116 aa, the metallic layer 116 ab,and the second conductive layer 116 ac, the thickness of each layer maybe set based on the metallic layer 116 ab.

This is because the metallic layer 116 ab, namely, the intermediatelayer, serves to determine an attachment (bonding) or contact area andserves as a reflection layer between the lower and upper layers, so itis advantageous to set the thickness of each layer based on the metalliclayer 116 ab.

Here, in forming the first electrode 116 a to have the structureincluding first conductive layer 116 aa, the metallic layer 116 ab, andthe second conductive layer 116 ac, the thickness ratio of respectivelayers may be substantially 1:9.5˜10:1.

The reason is because the first conductive layer 116 aa serves toimprove an adhesive strength with the lower interlayer insulating layer115, so it is formed to be thinner than the metallic layer 116 ab.

Also, the second conductive layer 116 ac may be formed to be thinnerthan the metallic layer 116 ab in order to minimize a problem thatchromaticity changes due to diffusion or diffraction of light reflectedfrom the metallic layer 116 ab serving as the reflection layer.

To form the tapered angle(s) of the source and drain electrodes or thatof the first electrode, a photolithography process may be used in whichone or more process parameters are varied. For example, the etchingconditions of a photoresist pattern may be different or varied.

As described above, in accordance with one or more embodiments, one ofmore of the source or drain electrodes or the first electrode may beformed as a multi-layer and the tapered angles of the layers may becontrolled to improve step coverage and contact interfacecharacteristics, resulting in an improvement of display quality and thereliability of the device Additionally, the source and drain electrodesmay have a triple-layer structure that includes the possibility ofTi/Al/Ti, or a double-layer structure that includes the possibility ofTi/Al.

In accordance with the embodiments described herein, the emitting layercause light to be emitted in various colors. In a case where theemitting layer emits red light, the emitting layer may include a hostmaterial including carbazole biphenyl (CBP) or 1,3-bis(carbazol-9-yl(mCP), and may be formed of a phosphorescence material including adopant material includingPIQIr(acac)(bis(1-phenylisoquinoline)acetylacetonate iridium),PQIr(acac)(bis(1-phenylquinoline)acetylacetonate iridium),PQIr(tris(1-phenylquinoline)iridium), or PtOEP (octaethylporphyrinplatinum) or a fluorescence material including PBD:Eu(DBM)3(Phen) orPerylene.

In the case where the emitting layer emits red light, a highest occupiedmolecular orbital of the host material may range from 5.0 to 6.5, and alowest unoccupied molecular orbital of the host material may range from2.0 to 3.5. A highest occupied molecular orbital of the dopant materialmay range from 4.0 to 6.0, and a lowest unoccupied molecular orbital ofthe dopant material may range from 2.4 to 3.5.

In the case where the emitting layer emits green light, the emittinglayer includes a host material including CBP or mCP, and may be formedof a phosphorescence material including a dopant material includingIr(ppy)3(fac tris(2-phenylpyridine)iridium) or a fluorescence materialincluding Alq3(tris(8-hydroxyquinolino)aluminum).

In the case where the emitting layer emits green light, a highestoccupied molecular orbital of the host material may range from 5.0 to6.5, and a lowest unoccupied molecular orbital of the host material mayrange from 2.0 to 3.5. A highest occupied molecular orbital of thedopant material may range from 4.5 to 6.0, and a lowest unoccupiedmolecular orbital of the dopant material may range from 2.0 to 3.5.

In the case where the emitting layer emits blue light, the emittinglayer includes a host material including CBP or mCP, and may be formedof a phosphorescence material including a dopant material including(4,6-F2 ppy)2Irpic or a fluorescence material including spiro-DPVBi,spiro-6P, distyryl-benzene (DSB), distyryl-arylene (DSA), PFO-basedpolymers, PPV-based polymers, or a combination thereof.

In the case where the emitting layer emits blue light, a highestoccupied molecular orbital of the host material may range from 5.0 to6.5, and a lowest unoccupied molecular orbital of the host material mayrange from 2.0 to 3.5. A highest occupied molecular orbital of thedopant material may range from 4.5 to 6.0, and a lowest unoccupiedmolecular orbital of the dopant material may range from 2.0 to 3.5.

Various color image display methods may be implemented in an organiclight emitting device such as described above. These methods will bedescribed below with reference to FIGS. 9A to 9C.

FIGS. 9A to 9C illustrate various implementations of a color imagedisplay method in an organic light emitting device according to anexemplary embodiment of the present invention.

First, FIG. 9A illustrates a color image display method in an organiclight emitting device separately including a red organic emitting layer201R, a green organic emitting layer 201G and a blue organic emittinglayer 201B which emit red, green and blue light, respectively.

The red, green and blue light produced by the red, green and blueorganic emitting layers 201R, 201G and 201B is mixed to display a colorimage.

It may be understood in FIG. 9A that the red, green and blue organicemitting layers 201R, 201G and 201B each include an electron transportlayer, an emitting layer, a hole transport layer, and the like. In FIG.9A, a reference numeral 203 indicates a cathode electrode, 205 an anodeelectrode, and 210 a substrate. It is possible to variously change adisposition and a configuration of the cathode electrode, the anodeelectrode and the substrate.

FIG. 9B illustrates a color image display method in an organic lightemitting device including a white organic emitting layer 301W, a redcolor filter 303R, a green color filter 303G and a blue color filter303B. And the organic light emitting device further may include a whitecolor filter (not shown).

As illustrated in FIG. 9B, the red color filter 303R, the green colorfilter 303G and the blue color filter 303B each transmit white lightproduced by the white organic emitting layer 301W to produce red light,green light and blue light. The red, green and blue light is mixed todisplay a color image.

It may be understood in FIG. 9B that the white organic emitting layer301W includes an electron transport layer, an emitting layer, a holetransport layer, and the like.

FIG. 9C illustrates a color image display method in an organic lightemitting device including a blue organic emitting layer 401B, a redcolor change medium 403R and a green color change medium 403G.

As illustrated in FIG. 9C, the red color change medium 403R and thegreen color change medium 403G each transmit blue light produced by theblue organic emitting layer 401B to produce red light, green light andblue light. The red, green and blue light is mixed to display a colorimage.

It may be understood in FIG. 9C that the blue organic emitting layer401B includes an electron transport layer, an emitting layer, a holetransport layer, and the like.

A difference between driving voltages, e.g., the power voltages VDD andVss of the organic light emitting device may change depending on thesize of the display panel 100 and a driving manner. A magnitude of thedriving voltage is shown in the following Tables 1 and 2. Table 1indicates a driving voltage magnitude in case of a digital drivingmanner, and Table 2 indicates a driving voltage magnitude in case of ananalog driving manner.

TABLE 1 VDD-Vss VDD-Vss VDD-Vss Size (S) of display panel (R) (G) (B) S< 3 inches 3.5-10 (V)  3.5-10 (V)  3.5-12 (V)  3 inches < S < 20 inches5-15 (V) 5-15 (V) 5-20 (V) 20 inches < S 5-20 (V) 5-20 (V) 5-25 (V)

TABLE 2 Size (S) of display panel VDD-Vss (R, G, B) S < 3 inches 4~20(V) 3 inches < S < 20 inches 5~25 (V) 20 inches < S 5~30 (V)

An exemplary embodiment of the present invention provides an organiclight emitting device capable of improving a step coverage of wirings orelectrodes.

In an aspect, an organic light emitting device comprises a transistorpositioned on a substrate and including gate, source, and drainelectrodes, a first electrode connected with the source or the drainelectrode; an emitting layer positioned on the first electrode; and asecond electrode positioned on the emitting layer, wherein the sourceand drain electrodes comprise first, second, and third layers,respectively, and the first, second, and third layers have eachdifferent tapered angle. And the first electrode includes a metalliclayer and a conductive layer, and a tapered angle of the metallic layeris different from that of the conductive layer.

In another aspect, an organic light emitting device comprises atransistor positioned on a substrate and comprising gate, source, anddrain electrodes, a first electrode connected with the source or thedrain electrode, an emitting layer positioned on the first electrode anda second electrode positioned on the emitting layer, wherein the sourceand drain electrodes comprise first, second, and third layers,respectively, tapered angles of the first, second, and third layers aredifferent from each other. And the first electrode includes a firstconductive layer, a metallic layer and a second conductive layer, and atleast one or more tapered angles among tapered angles of the firstconductive layer, the metallic layer and the second conductive layer aredifferent from each other.

In still another aspect, an organic light emitting device comprises atransistor positioned on a substrate and including gate, source, anddrain electrodes, a first electrode connected with the source or thedrain electrode, an emitting layer positioned on the first electrode anda second electrode positioned on the emitting layer, wherein the firstelectrode comprises a metallic layer and a conductive layer, and atapered angle of the metallic layer and that of the conductive layer aredifferent.

In still another aspect, an organic light emitting device comprises atransistor positioned on a substrate and including gate, source, anddrain electrodes, a first electrode connected with the source or thedrain electrode, an emitting layer positioned on the first electrode anda second electrode positioned on the emitting layer, wherein the firstelectrode includes a first conductive layer, a metallic layer, and asecond conductive layer, and at least one or more tapered angles amongtapered angles of the first conductive layer, the metallic layer, andthe second conductive layer are different.

Any reference in this specification to “one embodiment,” “anembodiment,” “example embodiment,” etc., means that a particularfeature, structure, or characteristic described in connection with theembodiment is included in at least one embodiment of the invention. Theappearances of such phrases in various places in the specification arenot necessarily all referring to the same embodiment. Further, when aparticular feature, structure, or characteristic is described inconnection with any embodiment, it is submitted that it is within thepurview of one skilled in the art to effect such feature, structure, orcharacteristic in connection with other ones of the embodiments.

Although embodiments have been described with reference to a number ofillustrative embodiments thereof, it should be understood that numerousother modifications and embodiments can be devised by those skilled inthe art that will fall within the spirit and scope of the principles ofthis disclosure. More particularly, various variations and modificationsare possible in the component parts and/or arrangements of the subjectcombination arrangement within the scope of the disclosure, the drawingsand the appended claims. In addition to variations and modifications inthe component parts and/or arrangements, alternative uses will also beapparent to those skilled in the art.

1. An organic light emitting device comprising: a transistor on asubstrate, the transistor including gate, source, and drain electrodes;a first electrode connected to one of the source and drain electrodes;an organic emitting layer on the first electrode; and a second electrodeon the organic emitting layer, wherein each of the source and drainelectrodes includes first, second, and third layers each having adifferent tapered angle, the second layer being sealed by the first andthird layers, a thickness ratio of the first and second layers being1:2.25 to 1:22.5, wherein the first electrode includes a metallic layerand a conductive layer.
 2. The organic light emitting device of claim 1,wherein a tapered angle of the metallic layer lies in a rangesubstantially between 35° and 70°.
 3. The organic light emitting deviceof claim 1, wherein a tapered angle of the conductive layer lies in arange substantially between 70° and 90°.
 4. An organic light emittingdevice comprising: a transistor on a substrate, the transistor includinggate, source, and drain electrodes; a first electrode connected to oneof the source and drain electrodes; an organic emitting layer on thefirst electrode; and a second electrode on the organic emitting layer,wherein each of the source and drain electrodes includes first, second,and third layers each having a different tapered angle, the second layerbeing sealed by the first and third layers, a thickness ratio of thefirst and second layers being 1:2.25 to 1:22.5, wherein the firstelectrode includes a first conductive layer, a metallic layer, and asecond conductive layer.
 5. The organic light emitting device of claim4, wherein a tapered angle of the first conductive layer lies in a rangesubstantially between 50° and 90°.
 6. The organic light emitting deviceof claim 4, wherein a tapered angle of the metallic layer lies in arange substantially between 35° and 70°.
 7. The organic light emittingdevice of claim 4, wherein a tapered angle of the second conductivelayer lies in a range substantially between 70° and 90°.
 8. The organiclight emitting device of claim 4, wherein a tapered angle of the firstlayer lies in a range substantially between 30° and 50°.
 9. The organiclight emitting device of claim 4, wherein a tapered angle of the secondlayer on the first layer lies in a range substantially between 50° and70°.
 10. The organic light emitting device of claim 4, wherein a taperedangle of the third layer on the second layer lies in a rangesubstantially between 70° and 90°.